Impact of nitrogen vacancies on the high temperature behavior of (Ti1−xAlx)Ny alloys

Substoichiometric solid solution alloys of cubic (Ti1−xAlx)Ny with x = 0.26, 0.48 and 0.60, and y ranging from 0.93 to 0.75 were grown by cathodic arc deposition. The influence of nitrogen deficiency on their thermal stability was studied by X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy, and atom probe tomography. The nitrogen deficiency did not significantly affect the columnar growth nor the as deposited hardness. At elevated temperatures, alloys with x = 0.48 and 0.60 decompose isostructurally into cubic c-TiN and cubic c-AlN domains, which is consistent with spinodal decomposition. The decomposition is retarded by decreasing the nitrogen content, e.g. the formed isostructural domains in (Ti0.52Al0.48)N0.92 at 900 °C are similar in size to (Ti0.52Al0.48)N0.75 at 1200 °C. The formation of hexagonal w-AlN is shifted to higher temperatures by decreasing nitrogen content. Nucleation and growth of Al-Ti clusters in a Ti rich matrix were observed for the alloys with high Ti content, x = 0.26. These results suggest that nitrogen deficiency reduces the driving force for phase separation.

Graphical abstractImpact of nitrogen vacancies on TiAlN thin films. Reconstructed 3D APT tips of (Ti0.52Al0.48)Ny, with y = 0.92, 0.87 and 0.75, after heat treatment at 1200 °C.Figure optionsDownload full-size imageDownload high-quality image (1097 K)Download as PowerPoint slide